This invention relates to a shadow mask support member (e.g. a spring comprising parallel bonded sheets) for supporting a shadow mask in a color Braun tube (cathode ray tube) so as to correct a color drift, and also relates to a method of producing such a support member.
In a color Braun tube of a television set, when a shadow mask is heated by electron beams, the shadow mask is thermally expanded to produce a color drift trouble. Therefore, there has heretofore been used a support member for resiliently support the shadow mask relative to a glass container, such a support member comprising a spring of a bimetal composed of two metal plates, which have thermal expansion coefficients different to each other, bonded parallel together on their marginal surfaces. Typically, such a spring has been formed by stamping and shaping a bimetal (or a trimetal) which has a low-expansion plate of an invar alloy (Fe-36Ni) and a high-expansion plate of austenitic stainless steel such as SUS304 (Fe-18Cr-8Ni).
Recently, with an increased size of television sets, there is a tendency for a Braun tube to increase in size and to become flatter. On the other hand, a shadow mask support member has been required to have a high-strength, compact design. In the case of the conventional parallel bonded-type bimetal formed by combining SUS 304 and a Fe-36% Ni invar alloy together, the tensile strengths of SUS304 and the invar alloy at a room temperature are about 120 kgf/mm.sup.2 and about 80 kgf/mm.sup.2, respectively, even if an aging treatment is effected after cold working. Particularly, the strength of the invar alloy is low. Thus, the conventional support member is not sufficiently high in strength to have a compact design, and therefore there has been encountered a problem that the support member can not be of a sufficiently small size. Under the circumstances, the parallel bonded-type bimetal, constituting the support member, has now been required to have a higher strength, and therefore the metal plates, constituting the parallel bonded-type bimetal, have been required to have a high strength.
When the shadow mask is to be incorporated into the Braun tube, the support member, while subjected to a strain, undergoes a heat history several times at temperatures ranging from 400.degree. C. to 600.degree. C. If the support member is formed into a small size, there is a possibility that the support member is permanently deformed by the heat of this heat history. The support member, constituted by the conventional parallel bonded-type bimetal (i.e., the combination of SUS304 and the Fe36%Ni invar alloy), does not possess a sufficient resistance to thermal deformation, and therefore there has been encountered a problem that the support member can not have a small-size design. Therefore, the parallel bonded-type bimetal, constituting the support member, has also been required to have an excellent resistance to thermal deformation, and to achieve this, it has been desired that the metal plates, constituting the parallel bonded-type bimetal, should have an excellent resistance to thermal deformation.
As described above, in order that the Braun tube can have a large-size, flat design, there has been a demand for the type of shadow mask support member having a high strength and an excellent resistance to thermal deformation.